The present invention is directed to determining a state of a dielectric material by determining a similarity or dissimilarity between: (a) a derived set of impedance values obtained from signals output by a capacitor having the dielectric material therein, and (b) one or more predetermined sets of impedance values, each such set indicative of a possible state for the dielectric material. In particular, each of the derived and predetermined sets has impedance values for a common plurality of electrical frequencies used to excite the capacitor. Each of the sets is presumed to correspond to a time interval that is sufficiently short so that the dielectric material is expected to remain in substantially the same state during the time interval.
In many circumstances the quality of material(s), and/or the evaluation of a process of manufacturing material(s) can be determined by the unique responses of the material(s) to electrical currents flowing therethrough. In particular, electrical impedances of such a material(s) may be used to identify changes and/or differences in the dielectric of the material(s). Thus, during a manufacturing process, the monitoring of dielectric changes of a manufactured item has been used to determine whether the manufacturing process is producing items having desired characteristics. For example, in U.S. Pat. No. 5,219,498 by Keller et al., composite materials having fibers impregnated with polymeric matrices are cured or thermoformed in a heating system. While the composite material is curing, capacitance and conductance samplings are taken, over an extended time, and the shape or geometric characteristics of the curve(s) generated by the samples (e.g., topographical features) are used to determine whether the curing process is progressing as expected, or whether appropriate modifications to the process need to be timely introduced for yielding a high quality product from the curing process. For example, a rule base is used to identify such geometric curve characteristics. In particular, the Keller patent attempts to identify geometric curve characteristics such as peaks, valleys, flats, rises and falls, and if identified, then those geometric characteristics are used to determine the state or condition of the dielectric material. Accordingly, complex pattern matching techniques can be required to identify such geometric curve characteristics. Additionally, sampling frequency adjustments can be required to detect such relative curve characteristics. For example, the time sale can be critical in the Keller patent since it is concerned with, e.g., rates of change and whether such changes are negative or positive, or changing between negative and positive. Thus, substantial time and/or computational resources can be expended in determining a similarity between actual and desired geometric curve characteristics.
In many contexts, however, it is desirable to determine the state of a dielectric material by directly comparing capacitive and/or conductive response values to corresponding reference capacitive and/or conductive values for one or more electrical frequencies. Moreover, it is desirable to determine state capacitive and conductance (i.e., impedance) information regarding a dielectric material in substantially real-time and/or with reduced computational capabilities. Furthermore, it is desirable to determine such state information without concern for timing adjustments needed for matching geometric characteristics determined over an extended time period. Thus, it would be desirable to have a simpler, more efficient and substantially non-time scale dependent system for using dielectric related values of a material to thereby determine a state or condition of the material, and in particular, for a material whose condition needs to be determined in substantially real-time.
The present invention is a method and system for identifying a condition or state of a dielectric material (such as an, item of manufacture, or substance) by analyzing a xe2x80x9csignaturexe2x80x9d of impedance related values for the dielectric material, wherein the values are derived from impedances of a range of one or more electrical frequencies applied to the dielectric material, and subsequently the values are compared to one or more sets of reference values. For example, such dielectric materials may include vulcanizates, resins, lubricating fluids, water, medical solutes, pharmaceuticals, and bulk chemicals such as isocyanates, polyurethanes, formaldahydes, epoxies, and phenolics that may be evaluated with the present invention for thereby: (a) changing a production process, (b) determining a contaminant level of such a dielectric material, or (c) identifying that a desired characteristic exists in the dielectric material.
The present invention determines such an impedance signature as a collection of discrete conductivity and capacitance values for each of a plurality of frequencies, wherein each of the values is obtained substantially simultaneously from a dielectric material being analyzed. Accordingly, the resulting impedance signature is similar to a xe2x80x9cbarcodexe2x80x9d, in that, for each frequency applied to the dielectric material, at least one of a conductivity and a capacitance (i.e., impedance) related value is obtained. Accordingly, for determining a state or condition of the dielectric material, the barcode analogy for such impedance signatures may be even further strengthened by representing each of the impedance related values as a value on a common predetermined impedance scale. Moreover, the resulting aggregate collection of impedance related values are compared to one or more predetermined such impedance barcodes having corresponding conductivity/capacitance related values for the same frequencies, wherein each such predetermined impedance barcode includes or identifies impedance related values indicative of a corresponding possible condition or state of the dielectric material. Thus, an impedance barcode obtained from the dielectric material may be compared with one or more of the predetermined impedance barcodes for determining similarities and/or differences between the barcodes. Thus, instead of determining a condition of a dielectric material by identifying and comparing geometric characteristics (e.g., peaks, valleys, rises, falls, etc.) of a curve obtained from pairs of points (t, imp), where imp is an impedance value and t is a corresponding sampling time, the present invention compares, for each of one or more of electrical frequencies: (a) one or more corresponding values, v, related to actual impedance responses obtained from the dielectric material being assayed with (b) one or more corresponding predetermined or designated impedance values Vr that serve as reference values. Note, that unless otherwise stated, the terms xe2x80x9cpredetermined impedance valuexe2x80x9d and xe2x80x9cdesignated impedance valuexe2x80x9d will be used interchangeably. The meaning intended by both terms is the combination of their meanings; i.e., a predetermined or designated impedance value that serves as a reference value for comparing with a derived impedance value for the same frequency.
More generally, an apparatus embodying the present invention can be characterized as having the following components (1.1) through (1.5) following:
(1.1) a repository for storing, for each of one or more predetermined possible states for a dielectric material, a corresponding set of designated impedance related values for the dielectric material, wherein for each of a plurality of electrical frequencies, one of said designated impedance related values is provided in said corresponding set, such that said designated impedance related values of said set are collectively indicative of the predetermined possible state of the dielectric material;
(1.2) a capacitor having first and second spaced apart capacitor plates and a dielectric material therebetween;
(1.3) a signal generator and a load resistor electrically connected in series to said first capacitor plate for exciting said capacitor, wherein said signal generator, in combination with said load resistor provide, for each of said plurality of electrical frequencies, a corresponding current at the frequency to said capacitor; wherein each of said corresponding currents is provided to said capacitor within a time interval that is sufficiently short so that the dielectric material is expected to remain in a same one of said predetermined possible states during said time interval;
(1.4) amplification and digitization components for: (a) receiving, for said electrical frequencies input to said capacitor, responsive signals from said capacitor, each said responsive signal indicative of an impedance of the dielectric material, and (b) amplifying and digitizing said responsive signals, thereby obtaining a plurality of derived impedance related values, wherein there is at least one of said derived impedance related values for each of said electrical frequencies; and
(1.5) one or more analysis components for determining, for at least one of said predetermined possible states, one of a similarity and a dissimilarity between said derived impedance related values and said corresponding set of designated impedance values.
Moreover, it is an aspect of the present invention to perform the following steps:
(2.1) for each of one or more possible conditions, performing the following step (a):
(a) establishing, for the possible condition, a corresponding set of designated impedance related values, wherein for each of a plurality of electrical frequencies, one of said designated impedance related values is provided, such that said designated impedance values of said set are collectively indicative of the possible condition of the dielectric material;
(2.2) providing, for each of said plurality of frequencies, an electrical current to a capacitor having the dielectric material disposed between first and second capacitor plates of said capacitor, thereby obtaining an electrical signal response from said capacitor indicative of an impedance response by said dielectric material to said frequency; wherein said signal responses are collectively identified as being received from said capacitor at a substantially identical time sufficiently short so that the dielectric material is expected to remain in a same one of said possible conditions during said time interval;
(2.3) obtaining, for each of said frequencies, a derived impedance measurement for said electrical signal response to said frequency, and thereby obtaining a plurality of said derived impedance measurements for said substantially identical time;
(2.4) determining, for at least one of said possible conditions, one of a similarity and a dissimilarity between: (a) said corresponding set for the at least one possible condition, and (b) said plurality of said derived impedance measurements;
wherein a result from said step of determining is indicative of whether or not the dielectric material is in said at least one possible condition.
In at least one embodiment the present invention generates such impedance barcodes using a non-bridged single electrode that serves as a capacitor plate, and wherein the dielectric material to be analyzed is intermediate between this single electrode and some other planer or substantially planer conductive surface that can serve as the capacitor plate for pairing with the single electrode. Thus, with the present invention a capacitor can be created with the dielectric material to be analyzed provided between the two plates. In particular, the second plate of this capacitor may be a preexisting conductive surface that is used for the confining or forming of the dielectric material to be analyzed. For instance, the second plate of the capacitor for the present invention may be an electrically conductive portion of a tube, pipe or reservoir having a petrochemical therein (e.g., oil or hydraulic fluid) as the dielectric material to be assayed.
Regarding fluids such as petrochemicals, the present invention allows real time and/or continuous monitoring of impedance barcodes of the fluid for determining whether such barcodes vary sufficiently from one or more predetermined impedance barcodes so as to require activation of an alert signal and/or activation of an action for mitigating a change in the fluid indicated by the change in the impedance barcode. This embodiment of the present invention has significant advantages in, e.g., determining when to change oil or hydraulic fluids in engines or a vehicle. Typically such petrochemicals are changed according to a fixed maintenance schedule dependent upon some use related parameter such as mileage (for a vehicle), or the lapsed time since a last change. However, such criteria do not take into account the actual condition of the petrochemical. Thus, the present invention can be cost effectively provided within, e.g., motorized transports such as autos, buses, boats, trains, aircraft for more precisely indicating when such petrochemicals need to be changed.
Alternatively, the present invention may be used in determining the state-of-cure of a rubber product such as a gasket or seal by comparing the impedance barcodes of the cured rubber product sample to both an uncured reference sample and a 100% cured reference sample. Note that it is not uncommon for currently available prior art rubber cure analysis techniques to require a substantial time period, (e.g., 2-4 hours) for completing such a state-of-cure analysis. However, with the present invention, such an analysis may be performed in less than 20 minutes, and more preferably less than 5 minutes. Accordingly, by utilizing the present invention, substantially immediate corrective action can be initiated when the curing process is not proceeding as desired. Thus, in a production environment, such articles as tires, seals, bushings and other elastomeric components, the costly production of defective articles may be substantially alleviated by use of the present invention.
Additionally, other embodiments of the present invention may be used in medical diagnosis and analysis for determining impurities and/or contaminants in various fluids such as blood or urea. For example, for patients requiring kidney dialysis to remove impurities from their blood, such dialysis procedures are typically performed on a regularly scheduled basis regardless of the actual level of impurities in the patient""s blood. As a result, the fluctuation in impurities may be substantial between dialysis sessions. Accordingly, by attaching a portable embodiment of the present invention to the patient, a continuous determination of the accumulation of blood impurities may be monitored for determining when a next dialysis session is likely to be necessary.
Additionally, the present invention may be used for determining a duration of a dialysis session according to a near real time monitoring of the dialyzing fluid flowing both into and out of a dialysis equipment during a dialysis session. In particular, a first capacitor according to the present invention may be provided to obtain impedance barcodes of clean dialysis fluid prior to entering the dialysis equipment, and a second capacitor according to the present invention may be used to obtain impedance barcodes of dialysis fluid exiting the dialysis equipment. Thus, the impedance barcodes of the incoming clean dialysis fluid may be used as a dynamic reference for comparing against impedance barcodes of exiting dialysis fluid for thereby determining when blood impurities in the exiting fluid are sufficiently low that the dialysis session can be terminated. Note that since such blood impurities may appear as ionic and dipolar abnormalities within the dialysis fluid, the impedance barcode differences between the reference impedance barcodes from the clean dialysis fluid, and the impedance barcodes of the exiting dialysis fluid may be statistically correlated so that, e.g., when such a correlation reaches a predetermined value (e.g., 99.5%), the removal of blood impurities is deemed to be essentially complete, and the dialysis session can be terminated.
Moreover, various other embodiments of the present invention may be used to continuously and/or in near real time monitor dielectric materials whose quality or purity is related to ionic and dipolar characteristics. For example, the present invention may be utilized for monitoring ground water purity, the purity of food products, the purity of pharmaceutical products, and for quickly identifying various types of contaminants within mass produced dielectric materials.
Since a non-bridged single electrode is the only sensing element provided by the present invention (as opposed to the two or three electrodes used in prior art systems), there is a substantially greater degree of flexibility regarding the physical orientation and position of this single electrode sensor for monitoring impedance barcodes of a dielectric material in the various embodiments of the present invention. In particular, an embodiment of the present invention may be more easily retrofitted onto pipes, or tubing in difficult to access places than prior art impedance measuring systems.
It is an aspect of the present invention that to obtain the impedance barcodes, the present invention provides a complex current for passing from the electrode sensor, through the dielectric material being monitored, and subsequently to the grounded second capacitor plate. In particular, the complex current is produced by a load resistor (RL) placed in series with the capacitor, wherein this current is subsequently provided by the electrode sensor to the dielectric material, and the second capacitor plate. Accordingly, a complex voltage is measured across the resistor with a high precision amplifier for obtaining the impedance barcode as will be described further hereinbelow. Subsequently, since a plurality of frequencies are applied to the electrode sensor, a plurality of discrete of conductivity and capacitance measurements may be obtained from the resulting complex voltage measured across the resistor. Moreover, in at least some embodiments of the present invention, there is no bridge circuit coupled to the capacitor. Accordingly, in these embodiments, such conductivity and capacitance values are relative conductivity and capacitance values (i.e., relative to some predetermined scale). Thus, this plurality of conductivity and capacitance values form a spectral response (i.e., an impedance barcode) for the dielectric material, and such a barcode can be compared with, e.g., a desired predetermined impedance barcode for thereby interfering that the dielectric material has a particular characteristic (desirable or undesirable).
It is a further aspect of the present invention that the predetermined one or more impedance barcodes (for comparing with impedance barcodes obtained from the dielectric material being monitored) are stored in a data storage unit accessible by and/or included in the present invention. In particular, such predetermined impedance barcodes may be retrieved and compared against impedance barcodes from the dielectric material being monitored, wherein the comparator may perform a statistical correlation between the two barcodes (e.g., a statistical correlation relating to a similarity or dissimilarity in the positions of the barcode values for the corresponding frequencies) for determining, e.g., a most likely state or condition of the dielectric material. Moreover, note that such a statistical comparison may be performed substantially faster and/or on less expensive devices than prior art curve shape pattern matching techniques. In various embodiments of the invention, the following statistical techniques may be used:
(3.1) analysis of standard deviation for performing the following steps with the derived and designated impedance values:
(1) establish a data file for the designated impedance values that contains the expected response for a plurality of frequencies;
(2) obtain a plurality of sample sets of derived impedance values, and determine if the derived values match the designated impedance values within some allowable range of standard deviation;
(3) make a determination of the purity/contamination/cure level based on the comparison.
(3.2) analysis of mean square error for performing the following steps with the derived and designated impedance values:
(1) establish a data file for the designated impedance values that contains the expected response for a plurality of frequencies;
(2) obtain one or more sample sets of derived impedance values, and determine if the derived values match the designated values within same allowable range of mean square error;
(3) make a determination of the purity/contamination/cure level based on the comparison.
(3.4) histogram analysis performing the following steps with the derived and designated impedance values:
(1) establish a data file containing histograms (distributions) of designated impedance values at a plurality of frequencies;
(2) obtain one or more sample sets of derived impedance value, and plot the values against the histogram to determine if the response is within a normal range;
(3) make a determination of the purity/contamination/cure level based on the comparison.
(3.5) analysis of correlation coefficients performing the following steps with the derived and designated impedance values:
(1) establish a data file containing the normal response of a material as designated impedance values, for a plurality of frequencies;
(2) obtain a sample of derived impedance values for the same frequencies;
(3) calculate the correlation coefficient (R2) between the data sets;
(4) use the R2 number to make a determination of purity/contamination/cure level.
In an alternative embodiment, instead of retrieving such a predetermined impedance barcode, a program element may be provided that has been trained to detect patterns of similarities and/or dissimilarities between such predetermined impedance barcode and the actual impedance barcode from the dielectric material being monitored. Note that such a trained program element may be, for example, an artificial neural network (ANN). Accordingly, the ANN (or other trainable component) may be trained using one or more sample sets of impedance related values (for predetermined electrical frequencies), wherein at least some of the sample sets are indicative of a corresponding predetermined condition or state of the dielectric material. Thus, during operation of the present invention, impedance values derived from the output of the capacitor may be input to the ANN for determining a most likely one of one or more conditions of the dielectric material. Additionally, an embodiment of the present invention may include an expert system having a rule base for identifying distinctive similarities and/or dissimilarities in the barcodes.
It is also an aspect of the present invention that in some embodiments, a predetermined impedance barcode for comparing with those impedance barcodes being monitored is such that this predetermined barcode may be for a particular undesirable characteristic of the dielectric material. Accordingly, the present invention may test for similarities between a current impedance barcode and such a predetermined undesirable barcode for thereby initiating corrective actions and/or generating alarm messages. Further, note that in one embodiment, data for both predetermined desirable and predetermined undesirable impedance barcodes may be used for training a learning program element so that such a program element may be able to recognize particular characteristics of the (near) real time impedance barcodes obtained from the monitoring process without a direct comparison with data from such predetermined impedance barcodes.
It is a further aspect of the present invention that an output from an impedance barcode identification component (e.g., an impedance barcode comparison component) for classifying or identifying an impedance barcode may be used for directly controlling a process that can change characteristics of the dielectric material being monitored. Thus, the present invention may provide feedback data for controlling such a process. For example, the feedback data may be provided to a process controller such as a process controller for a chemical production facility for monitoring a purity of a chemical being produced, or, e.g., for monitoring the contaminant levels of waste products being expelled into the environment.
To summarize, the present invention in various embodiments includes one or more of the following aspects:
(4.1) A system for analyzing the molecular constituents of various dielectric substances using a dielectric response therefrom wherein there is (are):
(4.1.1) A sensor that is a capacitor plate for a capacitor. Any other grounded conductive surface in proximity to the sensor may act as the other capacitor plate for the capacitor. The material under analysis must then be between (or pass between) these two capacitor plates. The material under analysis then becomes the dielectric in the capacitor. Therefore, a capacitor is formed by the material, the sensor, and the grounded secondary surface.
(4.1.2) A sensor excitation in the form of a low-level AC voltage that is applied to the sensor of (4.1.1). The frequency of the sensor excitation may be rapidly changed (in excess of 10 frequency changes per second), to produce a plurality of sensor responses in substantially real-time for one or more frequencies. The sensor response is dependent upon not only the applied one or more excitation frequencies, but more importantly, on the ionic and dipolar makeup of the material under analysis.
(4.1.3) An electrical circuit, including the formed capacitor comprising the sensor and the material under analysis that becomes a capacitive element in the circuit. It is an important aspect of the present invention that the electrical circuit is not a bridge network. Rather, current is driven to the grounded conductive surface through the material under analysis. This means that at least one embodiment of the present invention is a single electrode system, rather than a multiple electrode system (the latter being required in a bridge network). Note that the driven current becomes a complex current due to the fact that it passes through a complex impedance in the formed capacitor. The complex current is driven across a load resistor prior to the capacitor, creating a complex voltage having the necessary information to derive the capacitance and conductance responses. This complex voltage is then measured and amplified, and passed on to a computer analysis unit.
(4.1.4) One or more computer analysis units for receiving the complex voltage after it is captured and digitized with an analog to digital (A/D) converter. The digitized data is then analyzed by the computer analysis units, to produce both conductance and capacitance data for each of the previously mentioned one or more frequencies. Therefore, in substantially real-time, a xe2x80x9cbarcodexe2x80x9d of capacitance/conductance values is created representative of the impedance response of the material over a wide range of excitation frequencies. The computer analysis unit also contains a database, that stores one or more normal or expected responses, for the material under analysis (i.e., it contains prestored xe2x80x9cbarcodesxe2x80x9d that describe certain states of the material under analysis). The one or more computer analysis units then compare the prestored xe2x80x9cbarcodesxe2x80x9d with the measured xe2x80x9cbarcodexe2x80x9d. Based on this comparison, the computer analysis units make a determination about the state of the material. This determination may be: a determination of a purity, a determination of a contamination level, a determination of a cure state (such as in a vulcanizate), or any other physical effect which causes an ionic or dipolar change in the material under analysis.
(4.1.5) Various embodiments of the present invention may provide:
(4.1.5.1) The display of the derived barcodes wherein the display occurs to a human observer, substantially instantanenously after the one or more electrical frequencies are applied to the dielectric material;
(4.1.5.2) A common predetermined scale which upon substantially all of the derived impedance measurements have corresponding values.
(4.1.5.3) Both a capacitance and a conductance measurement for each electrical frequency instance applied to the dielectric material being assayed.
(4.1.5.4) A statistical comparison technique that may be performed between the stored and measured xe2x80x9cbarcodesxe2x80x9d of impedance responses, in order to make a determination regarding the state of the material under analysis. Moreover, the statistical comparison technique may include one or more of the following (a)-(d):
(a) determining mean square error in comparing the stored and measured impedance values,
(b) performing histogram analysis in comparing the stored and measured impedance values;
(c) performing a calculation of correlation coefficient between the stored and measured impedance values; and
(d) comparison of the stored and measured impedance values, with a certain standard deviation tolerance.
(4.1.5.5) A determination of at least one possible condition, wherein the condition is indicative of one of (a)-(c) following:
(a) a quality of a petrochemical in an engine;
(b) a cure state of a rubber compound;
(c) a characteristic of a bodily fluid.
(4.1.5.6) The dielectric material as one of a vulcanizate, a resin, a thermoset, a thermoplastic, an oil, water, a medical solute, a pharmaceutical, and a bulk chemical.
(4.1.5.7) A computer analysis unit(s) and comparison methodology that may contain a trainable component, such as an artificial neural network (ANN), wherein a trainable component (such as an ANN), is used to make determinations regarding the state of the material under analysis.
Other features and benefits of the present invention will become evident from the accompanying drawings and the detailed description hereinbelow.